1. Field of the Invention
The present invention relates to a pressure screen for cleaning a fibrous stock, and, more particularly, to a pressure screen having a screen element which is of rotationally symmetrical configuration about a screen axis and divides the pressure screen into an inlet chamber and an accepted stock chamber. The inlet chamber is connected at one axial end with a suspension inlet and at the opposite axial end with a reject outlet; and the accepted stock chamber is connected with an accepted stock outlet, and a rotor with rotor vanes is situated in the inlet chamber. The rotational axis of which rotor corresponds to the screen axis and which rotor rotates relative to the screen element. The rotor vanes are arranged distributed over a plurality of circumferential planes of the rotor which run perpendicular with respect to the rotational axis.
2. Description of the Related Art
Pressure screens are used in the preparation of fibrous stock suspensions, particularly in order to process the fibrous stock suspension in a wet screening process. For this purpose a pressure screen of this type includes a screen element that is provided with a multitude of apertures. The fibers contained in the suspension are intended to pass through the apertures in the form of accepted stock, whereas the undesirable solid components are repelled and are again directed out of the screen in the form of rejects.
It can also conceivably be used to separate different fiber components, in other words the shorter from the longer fibers.
Round apertures or slots are generally used as screening apertures. Generally, pressure screens of the type discussed herein are equipped with screen scrapers that have scraping surfaces moving along the screen. This prevents clogging of the screen apertures.
A screen scraper is known from WO 98/53135 that is equipped with blade elements for cleaning of the screen. These blade elements have a hydrodynamic profile that extends over the entire length of the screen element of a screen basket. Due to the relative movement relative to the surrounding suspension, the blade element exerts a pressure at the front and a suction impulse on the back upon the screen that is to be cleaned. Consequently a portion of the suspension that was rejected on the screen or has already passed the screen as accepted stock is sucked back, thereby keeping clear or clearing the screen apertures.
In contrast thereto, the rotor blades are formed for example by elevations in DE-OS 3701669.
What is needed in the art is a pressure screen to reduce the energy intake and the danger of clogging.